Dutch elm disease, caused by Ceratocystic ulmi (Buisman) C. Moreau, has killed millions of American elms since its first reported occurrence in the United States in 1930. The economic loss due to Dutch elm disease is estimated to be several billion dollars. Recommended control strategies for this disease have included destruction of vectors by sanitation and insecticide sprays, soil treatments to prevent root graft transmission, protective and therapeutic treatments with systemic fungicides, intensive surveillance and eradicative pruning, and resistant varieties of elm. While a single valuable tree might be protected by a combination of one or more of these strategies at a cost of several hundred dollars per year, no single control procedure has been completely effective.
Until recently, biological control of plant diseases has been directed more towards root diseases than disease of aerial plant parts, such as Dutch elm disease. Nevertheless, biological control of Fomes annosus (Fr.) Cke in the stumps of Scots pine by a second basidiomycete, Peniophora gigantea (Fr.) Masse, is an example of a very successful biological control involving an aerial plant part. Biological control of Dutch elm disease has been directed at the elm bark beetle vector and at the saprophytic stage of C. ulmi.
It is known that certain strains of Pseudomonas syringae produce broad spectrum antibiotics that are effective on a number of pathogenic bacteria and fungi when tested in vitro. This type of art is illustrated by U.S. Pat. No. 3,155,585 to De Vay; J. E. De Vay et al, Phytopathology, 58: 95-101 (1968); S. L. Sinden et al, Physiol. Plant Pathol., 1: 199-213 (1971); D. Gross and J. E. De Vay, Proc. Amer. Phytopathol. Soc. 3: 269-270 (1976); D. C. Gross et al, J. Appl. Bact., 43: 453-463 (1977); J. E. De Vay and G. A. Strobel, Phytopathology, 52: 360 (1962); and D. C. Gross and J. E. De Vay, Phytophathology, 67: 475-483 (1977). U.S. Pat. No. 3,155,585 also shows an in vivo effect in certain fruit trees of the antibiotic material formed by P. syringae.
The use of nystatin, an antifungal agent, to arrest Dutch elm disease in the tree is known. Exemplary of this type of prior art is R. J. Campana, Proc. Amer. Phytopathol. Soc., 3: 266 (1976). Also, it is known that certain strains of P. syringae exert an antimycotic effect against C. ulmi when tested in vitro. This type of prior art is illustrated by D. F. Myers, D. C. Sands and G. A. Strobel, Proc. Amer. Phytopathol. Soc., 12: 202 (1978).
However, this and the other prior art of which I am aware is deficient as failing to provide a method for treating Dutch elm disease that requires a single control procedure. Furthermore, this prior art fails to provide a single treatment procedure for the treatment of Dutch elm disease since retreatment is required.